1. Field of the Invention
This invention relates to terminally reactive polysilanes which are capable of accepting any desired functional group and useful as a source material for forming copolymers with other polymers. It also relates to a process for preparing the same.
2. Prior Art
Most industrial processes for preparing polysilanes utilize coupling reaction of dihalogenosilanes with alkali metals as reported in Journal of Polymer Science: Polymer Chemistry Edition, Vol. 22, 159-170 (1984), Journal of Organometallic Chemistry, Vol. 300, 327 (1986), and Journal of Polymer Science: Polymer Letter Edition, Vol. 21, 819 (1983). These processes produce polysilanes in the form of mixtures of cyclic polymers and halo- or hydrogen-terminated polymers. It is difficult to quantitatively obtain terminally modified polymers from these mixtures.
With respect to the synthesis of single end modified polysilanes, Sakurai et al. attempted living polymerization from polymers containing a disilane unit for introducing hydrogen or carboxylic acid as well as copolymerization of such polymers with polymethyl methacrylate (PMMA) as reported in Kagaku to Kogyo (Chemistry & Industry), Vol. 42, No. 4, 744. This attempt, however, has several industrial problems including limited type of substituents and limited availability of monomers.
Exemplary synthesis of terminally reactive polysilanes is reported in Journal of Organometallic Chemistry, Vol. 2, 478-484 (1964) and Journal of Organometallic Chemistry, Vol. 23, 63-69 (1970). More specifically, chloro-terminated oligosilanes can be prepared by reacting permethyloligosilanes with acetyl chloride in the presence of aluminum chloride. Also chloro-terminated oligosilanes can be prepared by reacting phenyl-terminated oligosilanes with hydrogen chloride or chlorosilane in the presence of aluminum chloride. These chloro-terminated oligosilanes, however, have a low degree of polymerization.
Focusing on the reaction that on exposure to ultraviolet (UV) radiation, polysilanes decompose and convert to those of a lower molecular weight while yielding highly reactive silylene and silyl radicals as reported in Applied Organometallic Chemistry, Vol. 1, 7-14 (1987), the inventors found that when high-molecular weight polysilanes are photodecomposed by selecting a chlorinated hydrocarbon as a solvent prone to chlorine withdrawal and exposing the polysilanes to UV radiation in the chlorinated hydrocarbon, silyl radicals generate and then form chloro-terminated polysilanes having a high degree of polymerization (see Japanese Patent Application No. 30103/1992 or U.S. Ser. No. 08/006,487).
We also found that by reacting chloro-terminated polysilanes with LiAlH.sub.4 for reduction, there are obtained hydro-terminated polysilanes having a high degree of polymerization, which have never been reported of synthesis (see Japanese Patent Application No. 223372/1992 or U.S. Ser. No. 08/096,259).
The term chloro- or hydro-terminated means that the polysilane is terminated with chlorine or hydrogen at both ends of its molecular chain unless otherwise stated.